Notional - a. 1. Imaginary; ideal; existing in idea only; visionary; fantastical.
2. Dealing in imaginary things; whimsical; fanciful.
I know this word doesn't exactly fit the parameters of the challenge - I mean, how obscure can a word be if it's used in the Wall Street Journal? Not to mention that it's a pretty obvious, straightforward variant of "notion" - but it'll have to do. It was either notional or words like "nut-breaker," for which the definition was: [See Nutcracker]. And the definition of "nutcracker" is "an instrument used to crack nuts." Oh yes. There are days when I just want to tell my dictionary, "Really? That's all you have for me?"
So, notional it is. The entymology can be traced back to the 1590s, where it originated from the Latin notionalis, which in turn came from notus. The whimsical, or "full of whims," meaning didn't appear until 1791. Why that is, I have no idea, but it's interesting nonetheless. It seems to be used most often to discuss theological or economic concerns. St. Thomas Aquinas used it a number of times in his systematic theology, but I didn't take the time to transcribe them from GoogleBooks, especially since the context gets really confusing. The economic usage appears to be the modern use of the word as it appears in a number of newspaper and magazine articles discussing various economic issues.
Personally, I prefer the examples included in both Webster's 1828 Dictionary and
The Imperial Dictionary of the English Language. Two tiny sentences, by one Prior and one Bentley, are given right below the definition of this word. I tried to find something out about these two men, but my searches came out dry. Apparently, they were known and respected enough to be included in dictionary, but not famous enough to stand out to Google. Anyway, Prior uses it this way: "notional good, by fancy only made." And Bentley says this: "A notional and imaginary thing." Webster himself adds, "as a notional man" to the entry.
I think it's a great word that could easily be introduced back into the literary realm. There's no need for it be sequestered off for economic theorists. Fiction writers, by definition, are notional. We deal in the imaginary, in the fanciful. Our aim though is to take the notional, put it on paper, and thereby make it something that exists in actual form instead of something that exists "in idea only."
And now to use it myself...
"I was in the midst of deciphering the last scrawled line on the page when another book came crashing down on top of it. I jerked upright and coughed at the dust that puffed out of the decaying pages. Egbert braced his arms on the table and leaned towards me, his smile smug, his eyes mocking.
"Was that necessary?" I moved the volume off my open pages.
"I got your attention."
"What do you want?"
"I don't want anything. Father wants to speak to you. And Mother wants you to eat."
"Father wants to speak to me? Are you sure?"
He scowled. "Yes, I'm sure. Apparently, he's decided there's something of value in that notional mind of yours."
"Well." I took the candle and started for the door through the maze of stacked books and scattered scrolls. "I hope my notions don't disappoint."
"As do I, little brother."